A lot of worlds over 1g gravity. How do 1G thrust ships take off?

[Anonymous]

Even a paltry 1 g thrust is quite a lot by current aircraft standards. E.g. a A380 has a max take off weight of ~575 tonnes and a thrust of 1400 kN, so can achieve flight with thrust to mass ratio of ~0.24 g. Of course it has much bigger wings (per mass) than any Traveller spacecraft I have seen.

A Starfighter (with rather small wings) could take off with a mass of 13 tonnes and a thrust of 44 kN (dry), for a thrust to mass ratio of about 0.34 g.

Yes, but it needs a runway and as we've seen, Free Traders don't have wheels. I think we should forget about unassisted aerodynamic take-off. It's hideously against all the lore.

 

[AnotherDilbert]

However, changing load should change the acceleration. I can't wait for the new rules that require recalculating acceleration every game turn as you burn off fuel.

It's quite simple, you use Tsiolkovskys Rocket Equation:

Something for the next FF&S?

 

[Anonymous]

It's quite simple, you use Tsiolkovskys Rocket Equation:

That assumes a reaction drive.

 

[AnotherDilbert]

Yes, but it needs a runway and as we've seen, Free Traders don't have wheels. I think we should forget about unassisted aerodynamic take-off. It's hideously against all the lore.

Do you consider T5 "hideously against all the lore"?

 

[AnotherDilbert]

It's quite simple, you use Tsiolkovskys Rocket Equation:

That assumes a reaction drive.

It assumes that we continuously change mass (by expelling propellant) as we accelerate with constant thrust. I think the result is the same if we continuously change mass by burning fuel in a fusion reactor and radiating the resulting heat.

But of course it was a joke...

 

[Anonymous]

Do you consider T5 "hideously against all the lore"?

OK thats fair for T5 which I don't own. What ships in Mongoose or T5 have wheels?

It's quite simple, you use Tsiolkovskys Rocket Equation:

That assumes a reaction drive.

It assumes that we continuously change mass (by expelling propellant) as we accelerate. I think the result is the same if we continuously change mass by burning fuel in a fusion reactor and radiating the resulting heat.

But of course it was a joke...

You've described a reaction drive (ejecting stuff & using newton's 3rd law to propel the ship via equal & opposite reaction). I was told the Traveller maneuver drive was reactionless, working by altering how gravity pulls on the ship. Confusingly, it also somehow emits enough particles to glow.

The equation determines your final speed after burning all your fuel. It's derived from the equations of conservation of momentum. It effectively states that the maximum speed of a space craft is some constant multiplied by the velocity of your drive's exhaust particles (assuming no in-flight refuelling) and it's only valid for drives that obey conservation of momentum. Reactionless drives violate conservation of momentum (they're impossible, like FTL). (edit: Possibly they don't violate it, but they don't use it, making the equation equally inapplicable. I can't tell you how they work as they don't exist).

Edit 2: I just realised that if the maneuver drive indeed works by altering the force of gravity on a ship, the mass of the ship is irrelevant (all objects fall at the same speed in the same gravity), and using displacement implies that the drive affects evetything in an area equally.

 

[AnotherDilbert]

What ships in Mongoose or T5 have wheels?

Neither T5 nor MgT2 describes any spacecraft in that much detail, I believe. (Even if the T5 design system does go into that specific detail.)

You've described a reaction drive (ejecting stuff & using newton's 3rd law to propel the ship via equal & opposite reaction).

OK, it was a long time ago that I worked trough the maths, but I believe that mathematically the constraints are that we accelerate with constant thrust and continuously decreasing mass, hence increasing acceleration. The same can theoretically be said for a Traveller spacecraft, even if the mass decrease is trivially small.

I was told the Traveller maneuver drive was reactionless, working by altering how gravity pulls on the ship. Confusingly, it also somehow emits enough particles to glow.

Exactly how this works is not clear...

I assume that Traveller M-drives are "reactionless" as in not a rocket that expels propellant, but not reactionless in a Physics sense (as in causing no reaction whatsoever).

From wiki:
"A reactionless drive is a device producing motion without the exhaust of a propellant. A propellantless drive is not necessarily reactionless when it constitutes an open system interacting with external fields, ..."
https://en.wikipedia.org/wiki/Reactionless_drive

If the M-drive interacts with the gravity field to produce thrust, and that produces an opposite reaction on the gravity field (and hence local planets), then momentum is conserved and physics isn't bent into a pretzel. I prefer that interpretation.

 

[AnotherDilbert]

I just realised that if the maneuver drive indeed works by altering the force of gravity on a ship, the mass of the ship is irrelevant (all objects fall at the same speed in the same gravity), and using displacement implies that the drive affects evetything in an area equally.

No, M-drives, sometimes called thruster plates, produce force, thrust, on the drive itself, it does not modify the local gravity field to cause the ship to "fall" into the field.

This new, artificially generated force pushes against a vessel's "thrust plates" themselves, ...

 

[phavoc]

There is a nice primer on aerodynamic lift by the boys at Glenn (e.g. NASA) - https://www.grc.nasa.gov/www/k-12/airplane/presar.html

There are a few inherent problems. First is that aircraft are built of aluminum, titanium, carbon fiber, but not crystalline steel or worse, collapsed matter plating. Lift is a force, and regardless of what you want to call it, the basic formula if F=M x A. And essentially a Traveller starships, even unloaded, built with crystalline steel, is going to be too heavy to generate enough lift. And, contrary to popular opinion, a brick is still a very un-aerodynamic object, and if you are going to try to say you have lift, you have to also say the shape of the object will not generate any lift, let alone the issue of the air in front becoming more dense the faster it goes. And compressed enough that atmosphere is going to become a literal wall.

Yes, landing strips support winged ships. I don't care what Miller says, mass is greater than wishing. But you notice how easily this entire issue goes away with the idea of starships using contragravity devices to cancel out the local gravity field. And THEN, and only THEN, does the Traveller universe come back into some semblance of a place where the handwavium isn't so bad that you can see through all the waving hands.

Since we had Repulsors in HG, that wasn't much of a problem?

You missed the statement where it was to assist ships that were too heavy to take off on their own? And no, the repulsor concept was fine as it stood.

Isn't that a question of enough thrust? Enough thrust gives enough speed gives enough airflow over the wings to lift with fairly small wings? (And some artistic licence in the illustrations?)

Even a paltry 1 g thrust is quite a lot by current aircraft standards. E.g. a A380 has a max take off weight of ~575 tonnes and a thrust of 1400 kN, so can achieve flight with thrust to mass ratio of ~0.24 g. Of course it has much bigger wings (per mass) than any Traveller spacecraft I have seen.

A Starfighter (with rather small wings) could take off with a mass of 13 tonnes and a thrust of 44 kN (dry), for a thrust to mass ratio of about 0.34 g.

That's not how physics works. An A380 (or bettern an AN-225) utilize the equation rooted in reality - Lift = coeffecient x ((density x velocity squared)/2) x wing area. If by Starfighter you are referring to the F-104, yes indeedy it flew, and flew fast! It was an interceptor, which sometimes was referred to as a rocket with wings. But you'll notice that it's areodynamic structure generated crappy lift (which was why it had such a high landing speed). It had a high takeoff speed (about 220mph), crappy glide ratio without thrust. Thrust to weight ratio is telling, but it's not necessarily a good measure. A F104G is .72 (with basic loadout), Harrier GR7 is .92, F-22 is 1.18, and the F-15K is 1.29. The A380 is .23 to 1.

All these aircraft utilize normal physics to take off. And none of them are built with crystalline steel, either.

Agreed, but T5 very specifically overrules such petty concerns...

Wings gives the benefit "Wings increase the performance of a ship’s Maneuver or Gravitic Drive +1G if operating in Atmosphere". (T5.09, p277)

T5 can be as silly as it wants, that's the benefit of making rules for a game. However that still doesn't make it possible (or any less probable). Oh, and to poke another stick into the rules miasma. The book says a Mercenary cruiser is unable to enter the atmosphere. However a modular cutter can? I'm sorry, but the hull of a cutter would not be able to generate any lift. And if we wanna take this all the way back to CT (and a few other versions) the cutter module could be dropped on a planet and the cutter could "fly" back with a giant gaping, very non-lifting, gap in the middle. Umm, can you say anti-grav lifting?

Since a ship with M-2 can achieve 2 g in free space it can produce enough thrust to overcome 1 g twice over by definition.

It's just a simplification in the system not to consider mass, but just volume, when dimensioning drives. Not even TNE FF&S dared dimension the thrusters on mass even if that clearly was the basic rule.

See, the inherent problem with this is that G-rating is already a handwavium. Thurst is measured in lbs/kilograms. In an aircraft with 35,000lbs of thrust you can make an 8G turn. Translating G-ratings into thrust is kinda hard since we have nothing in which to base them by. A rocket such as a Saturn-V has 7.6 million lbs of thrust. It weighs, at launch, 6.5 million lbs. Rocket equations don't translate into an object taking off horizontally.

The design system doesn't take mass into account, just volume. Do you ever wonder why that was? With anti-grav you can dismiss mass. As long as you can cram crap into your starship you only need to worry about volume and never how much it weighs (in a grav field) or masses (in space). Then you can make a ship that masses 100 tons vs a 10km long ship that masses a trillion tons both move at the same speed. Being able to ignore mass, even on a sliding scale, makes for a lot of wonderful spacecraft possibilities.

No, not if we have enough thrust from the M-drive. Or aerodynamic lift.

(Only TNE used contragrav; CT, MT, MgT, and even T5 uses anti-grav, there is a small but significant difference.)

So to take off vertically you need more thrust than your weight. To take off horizontally you can cheat and add in lift. As mentioned above, if you wanna talk about lift then you need to include things like aerodynamics and drag. Very few Traveller ships are aerodynamic like an aircraft, thus drag worsens their lift to weight ratio. And more power is great (Tim "the tool man" Taylor can tell you all about MORE POWER!), but it won't solve everything.

However, contragrav / anti-grav does. Sure, like jump drives it's not possible with today's tech, but it solves the question of how ships take off without all the logical contortion of "but the rules don't explicitly state ships have antigrav for lift", or trying to say a scout ship can generate enough lift using it's hull (which if you refer to the equations by the boys at Glenn you'll see NONE of the ships can make that happen). And you don't even have to delve into the now non-canon repulsors.

I truly don't understand why there is so much resistance to a simple concept that makes a LOT of problems just vanish. Spacecraft users would be utter fools to not utilize the same tech that a G-Carrier does.

 

[Condottiere]

Only works if you open up the tanks to space.

 

[AnotherDilbert]

You missed the statement where it was to assist ships that were too heavy to take off on their own? And no, the repulsor concept was fine as it stood.

Quite, a repulsor weapon repulsing incoming missiles, or a repulsor launch booster repulsing ships from the starport. They both have the same effect, so are just as non-problematical?

That's not how physics works. An A380 (or bettern an AN-225) utilize the equation rooted in reality -
Lift = coeffecient x ((density x velocity squared)/2) x wing area.

OK, I'll take your word for it. Basically this means that for a given airframe Lift = constant × v² or as I guessed before enough speed means enough lift. The needed take off speed may be impractically high for small wings, but that is far from impossible.

This lets us estimate the needed wing area for a Subbie. At about 4000 tonnes it would need about 6 times the wing area of an A380 (designed for 650 tonnes) with the same take off speed. Since we have 4 times the thrust to mass ratio we can allow a much higher take off speed, say twice the speed of the A380, so about 500 km/h, thus generating 4 times the lift, hence needing 4 times smaller wings, for a total of 6/4=1.5 times the A380s wing of 845 m², so about 1300 m².

Guesstimating from deck plans and illustrations the Subbie as drawn has about 500 m² wing area, so about 2.5 times less than needed. That is not too bad for a design dimensioned by the rule-of-cool. Make the wing 50% longer and 50% wider we get 225% as much area and are in the ball-park of a usable wing. The wing-span is still only about 40-45 m, so not unreasonable.

So, generating enough lift to take off with a Subbie is far from impossible.

If by Starfighter you are referring to the F-104, yes indeedy it flew, and flew fast! It was an interceptor, which sometimes was referred to as a rocket with wings.

Yes, I meant the Widowmaker (yes, I know that's unfair). It made up for its small wing by having high thrust and a high take off speed. I believe that illustrates my point, which it why I used it as an example.

T5 can be as silly as it wants, that's the benefit of making rules for a game. However that still doesn't make it possible (or any less probable).

Much as I dislike calling the Scout a lifting body, I wouldn't go so far as calling it impossible.

A little over a hundred years ago or so physicists believed the Sun was powered by burning coal, since that was the most powerful reaction they knew about. Producing energy without chemical reactions was clearly impossible...

OK, that is a bad example in general, but as already pointed out in this thread even if we have nailed down the basics, we don't know nearly everything about fluid dynamics or aerodynamics in general. In a few thousand years we might learn a trick or two...

Improbable aerodynamic lift is nowhere near as impossible as anti-grav, jump drives, or the Empress Wave. And in the end MWM makes canon what he feels like.

However a modular cutter can? I'm sorry, but the hull of a cutter would not be able to generate any lift.
...
Umm, can you say anti-grav lifting?

The Cutter is not supposed to generate any aerodynamic lift. Its drives are quite powerful enough to generate any lift or thrust it needs. It is streamlined as in "nothing falls off while travelling at speed in atmosphere".

Why would it need another large and expensive drive when the existing M-drive is quite powerful enough?

See, the inherent problem with this is that G-rating is already a handwavium. Thurst is measured in lbs/kilograms.

There is no handwavium, just basic mechanics simplified by using a nominal mass rather than current actual mass.

Thrust is a force measured in N (Newton) or lbf if you want to be medieval. Mass is measured in kg or lb. You might be sloppy with that on Earth, but in space the difference is important.

The g-rating is acceleration in free space or by F=ma => F/m=a simply the thrust to mass ratio.

In an aircraft with 35,000lbs of thrust you can make an 8G turn.

Aircraft generally turn (accelerate to the side) by using the wings to press against the air, only helped by vectored thrust. To find the acceleration caused by a force you need the mass of the object. As far as I know you statement lacks any defined meaning. Or am I just completely misunderstanding?

Translating G-ratings into thrust is kinda hard since we have nothing in which to base them by.

The g-rating is by definition the trust to mass ratio, so it is trivial to find the thrust if we know the g-rating and the mass. From MT we know the approximate masses of standard starships as roughly 10 tonnes per Dton for unarmoured ships.

So, a Free Trader with 1 g at 200 Dt or approximately 2000 tonnes has a thrust of roughly 20 MN.

The design system doesn't take mass into account, just volume. Do you ever wonder why that was? With anti-grav you can dismiss mass.

No, anti-grav does not nullify gravity, just provides a force to offset it (lift), and that force is vectorable (just as M-drives) so it can provide forward thrust, not just lift.

The anti-grav drive must still be dimensioned for the carried mass, as specified by Striker and MT.

As long as you can cram crap into your starship you only need to worry about volume and never how much it weighs (in a grav field) or masses (in space).

No, anti-grav does not imply inertialess drive. That would be much more magical mere M-drives...

Then you can make a ship that masses 100 tons vs a 10km long ship that masses a trillion tons both move at the same speed. Being able to ignore mass, even on a sliding scale, makes for a lot of wonderful spacecraft possibilities.

But that is quite unnecessary. A thousand times as large a ship with a thousand times as large a drive (as specified by the drive percentages) producing a thousand times as much thrust would have the same thrust to mass ratio hence g-rating and would accelerate at the same rate. And the same for a trillion times as large a ship. No anti-grav needed, nor would it affect the mass of the ship hence the acceleration in space.

So to take off vertically you need more thrust than your weight. To take off horizontally you can cheat and add in lift.

Agreed. Obviously?

As mentioned above, if you wanna talk about lift then you need to include things like aerodynamics and drag. Very few Traveller ships are aerodynamic like an aircraft, thus drag worsens their lift to weight ratio. And more power is great (Tim "the tool man" Taylor can tell you all about MORE POWER!), but it won't solve everything.

Agreed, very few Traveller ships even tries to generate aerodynamic lift.

Just being streamlined does not necessarily imply wings or lift, just that it won't burn up in atmosphere. Except in MgT2...

However, contragrav / anti-grav does.
...
I truly don't understand why there is so much resistance to a simple concept that makes a LOT of problems just vanish. Spacecraft users would be utter fools to not utilize the same tech that a G-Carrier does.

Yes, anti-grav would be very convenient, but it is an unnecessary complication. Just like an aircraft that can land vertically, it is possible and can be useful in some specific roles, but generally it is unnecessary and to expensive for general use.

Spacecraft users would be utter fools to include anti-grav drives, since by MT they cost about as much tonnage, power, and money as an M-drive of the same rating. So, instead of a 1 g M-drive and a 1 g anti-grav drive you could just as well have a 2 g M-drive that worked everywhere, not just in a planetary gravity well.

And as I have tried to argue all along, a 2 g M-drive can be very useful, but can also be rather expensive...

... or trying to say a scout ship can generate enough lift using it's hull (which if you refer to the equations by the boys at Glenn you'll see NONE of the ships can make that happen).

I'm not saying it, MWM is specifically saying it.

Note that the standard Scut does not need it since it already have a 2 g M-drive.

 

[Anonymous]

I'm sorry, but the hull of a cutter would not be able to generate any lift.

So to be both correct and useless I should point out that if you roll the cutter it will generate lift via the magnus effect.

I truly don't understand why there is so much resistance to a simple concept that makes a LOT of problems just vanish. Spacecraft users would be utter fools to not utilize the same tech that a G-Carrier does.

Not a lot of people understand physics, nor do they want to. I gave up when I asked how many ships had wheels and got no answer. I took that as an admission that they used anti-grav lift on the runway. It's still possible that's an external system at the starport.

But practically, you're right: You'd probably install anti-grav even if your ship didn't need it, as it would your life easier in so many ways.

Especically true for adventure ships which are "supposed" to go to all those weird under-developed words that the big ships don't touch because there is no starport with repulsors to help you take off.

 

[Old School]

correct and useless

There's a lot of that around here.

I don't know about you, Moppy, but it's at this point in a thread that I usually regret having started it (see my seemingly innocent request for a ruling on missile countermeasures).

 

[AnotherDilbert]

I don't know about you, Moppy, but it's at this point in a thread that I usually regret having started it (see my seemingly innocent request for a ruling on missile countermeasures).

Ever heard of herding cats?

People will disagree with you and talk about their own hobby-horses, not only what you want to talk about. Isn't that what makes the forum interesting?


If you want a straight simple canon answer then ships don't generally have anti-grav in CT, MT, or MgT, they generally do have contra-grav in TNE and anti-grav lifters in T5. Other edition I have no idea about.

But many people want anti-grav in their ships, so use it, whatever canon says. So I try, with occasional success, not to be too dogmatic about it.

 

[phavoc]

I'm sorry, but the hull of a cutter would not be able to generate any lift.

So to be both correct and useless I should point out that if you roll the cutter it will generate lift via the magnus effect.

I truly don't understand why there is so much resistance to a simple concept that makes a LOT of problems just vanish. Spacecraft users would be utter fools to not utilize the same tech that a G-Carrier does.

Not a lot of people understand physics, nor do they want to. I gave up when I asked how many ships had wheels and got no answer. I took that as an admission that they used anti-grav lift on the runway. It's still possible that's an external system at the starport.

But practically, you're right: You'd probably install anti-grav even if your ship didn't need it, as it would your life easier in so many ways.

Especically true for adventure ships which are "supposed" to go to all those weird under-developed words that the big ships don't touch because there is no starport with repulsors to help you take off.

The boys at Glenn cover that one, too! https://www.grc.nasa.gov/www/k-12/airplane/lift2.html You also can get it from spinning a ball. Though I don't believe you can get enough lift to offset your mass - especially if you are a cutter that has dropped it's module (in all but the latest versions). Fair point though.

Utilizing wheels for a craft can be very useful for ground movement when you don't want/need to power the ship up to pull it around. I would suspect those ships that don't visit rough ports or non-starship landing zones could easily have wheels installed. I'm pretty sure that most people who design their ships don't even think about stuff like that, preferring to focus on the pew-pew! aspects. But details bring a ship to life more then the pew-pew! factor (in my opinion).

 

[Anonymous]

I don't know about you, Moppy, but it's at this point in a thread that I usually regret having started it (see my seemingly innocent request for a ruling on missile countermeasures).

Gaming is a waste of time, and posting about it is a waste of time and electricity.

Yet here we are.

 

[Condottiere]

I looked at the manoeuvre drive high technology options, and identified the orbital variant as being lifters, or the anti gravity motors that would be orientated downwards, and thus create buoyancy.

 

[Old School]

I don't know about you, Moppy, but it's at this point in a thread that I usually regret having started it (see my seemingly innocent request for a ruling on missile countermeasures).

Gaming is a waste of time, and posting about it is a waste of time and electricity.

Yet here we are.

Yep.

 

[phavoc]

Quite, a repulsor weapon repulsing incoming missiles, or a repulsor launch booster repulsing ships from the starport. They both have the same effect, so are just as non-problematical?

In CT repulsors did both.

OK, I'll take your word for it. Basically this means that for a given airframe Lift = constant × v² or as I guessed before enough speed means enough lift. The needed take off speed may be impractically high for small wings, but that is far from impossible.

This lets us estimate the needed wing area for a Subbie. At about 4000 tonnes it would need about 6 times the wing area of an A380 (designed for 650 tonnes) with the same take off speed. Since we have 4 times the thrust to mass ratio we can allow a much higher take off speed, say twice the speed of the A380, so about 500 km/h, thus generating 4 times the lift, hence needing 4 times smaller wings, for a total of 6/4=1.5 times the A380s wing of 845 m², so about 1300 m².

Guesstimating from deck plans and illustrations the Subbie as drawn has about 500 m² wing area, so about 2.5 times less than needed. That is not too bad for a design dimensioned by the rule-of-cool. Make the wing 50% longer and 50% wider we get 225% as much area and are in the ball-park of a usable wing. The wing-span is still only about 40-45 m, so not unreasonable.

So, generating enough lift to take off with a Subbie is far from impossible.

It' s not my word. It's physics word.

The design of the wing provides the capability of the lift. More precisely, the design of the craft specifies how much lift is possible - this includes the design of the wing, the drag coeffecient of everything else poking out on the hull, etc. Taken together it provides the lift. You'll notice aircraft are quite smooth to minimize drag and cut lift. I would also point out that the Type-R 'wings' are anything but aerodynamically designed. The wing roots are far too thick, and while winglets do provide for better aerodynamics, I'm not sure those would provide anything other than additional drag.

How do you know we have 4 times thrust to mass ratio? What is the output in thrust of an engine that produces G-thrust? At 4,000 tons (or 8,000,000 lbs) it's kinda heavy for a craft. A fully loaded A380 is 632 tons.

Looking at a comparsion image (https://www.google.com/imgres?imgur...5HgAhXiHzQIHZfqDokQMwhDKAUwBQ&iact=mrc&uact=8. The comparison to an A380 https://www.google.com/url?sa=i&rct...aw1247wLVy_V_xsOQ5hCR32u&ust=1548784201211199 shows the wing area is much larger for a craft that weighs 1/6th.

Yes, I meant the Widowmaker (yes, I know that's unfair). It made up for its small wing by having high thrust and a high take off speed. I believe that illustrates my point, which it why I used it as an example.

Oh, I don't think the moniker is unfair. It was a fair attribution for an aircraft that was unforgiving when it came to landing (let alone the 30% or more crash rate the Luftwaffe had... silly men, trying to make the F104 into a ground attack plane!). The wing itself was quite thin. And the tail also provided lift (so much in fact that the wings were canted 10% downwards to offset the additional lift). In the F-104 case the wings did provide lift, but the aircraft operated more like a missile than a plane. Missiles have very tiny wings that provide lift, but it's relatively negligible. Even helo's, with their subby wings, get lift (again negligible when it comes to what is keeping it aloft). Their glide capabilities due to the lift from their wings are horrible, thus the high speed the F-104 must endure when trying to land. It was a very unforgiving aircraft by aviation standards.

Much as I dislike calling the Scout a lifting body, I wouldn't go so far as calling it impossible.

A little over a hundred years ago or so physicists believed the Sun was powered by burning coal, since that was the most powerful reaction they knew about. Producing energy without chemical reactions was clearly impossible...

OK, that is a bad example in general, but as already pointed out in this thread even if we have nailed down the basics, we don't know nearly everything about fluid dynamics or aerodynamics in general. In a few thousand years we might learn a trick or two...

Improbable aerodynamic lift is nowhere near as impossible as anti-grav, jump drives, or the Empress Wave. And in the end MWM makes canon what he feels like.

This is one version of the scout (https://i.pinimg.com/originals/34/db/67/34db678d8a1a69f452df1909ddad92ea.jpg), and there are others, some more streamlined, others less. I don't disagree that a scout coming down through the atmosphere would be able to generate lift from it's body shape. But it's mass is going to offset any lift it could ever generate. Here is a pretty straightforward discussion of lift done by the guys/gals at MIT. http://web.mit.edu/16.00/www/aec/flight.html You will notice that weight and drag feature prominently in the discussion of lift.

The Cutter is not supposed to generate any aerodynamic lift. Its drives are quite powerful enough to generate any lift or thrust it needs. It is streamlined as in "nothing falls off while travelling at speed in atmosphere".

Why would it need another large and expensive drive when the existing M-drive is quite powerful enough?

Ok, so let's go with this. Just how does it land? How does it hover to drop off it's cargo? How does it pick UP it's cargo? I realize the gyrations you are going through to justify the point, but it could never land. So I will agree the cutter can fly. Tell me how it can do all the things it is supposed to do without anti-grav. And it would be nice to know how it fly's without the module present, too.

There is no handwavium, just basic mechanics simplified by using a nominal mass rather than current actual mass.

Thrust is a force measured in N (Newton) or lbf if you want to be medieval. Mass is measured in kg or lb. You might be sloppy with that on Earth, but in space the difference is important.

The g-rating is acceleration in free space or by F=ma => F/m=a simply the thrust to mass ratio.

No, it's a lot of handwavium. What is a 1-G rating in thrust? Using the formula you are stating mass is a requirement to answer the equation. So yeah, if you aren't using mass (or weight when in a grav field), then it's handwavium.

Aircraft generally turn (accelerate to the side) by using the wings to press against the air, only helped by vectored thrust. To find the acceleration caused by a force you need the mass of the object. As far as I know you statement lacks any defined meaning. Or am I just completely misunderstanding?

In the example I am citing I am illustrating the mish-mash of ratings. A ship has a 1-G thrust rating, but can handle a 8-G turn. So is the force the ship is receiving equivalent to 8x it's thrust? That's not the case when using thrust-to-weight ratios. Hence what does 1G thrust mean in the atmosphere? Since the question is about a ship generating lift it's germane to the discussion.

The g-rating is by definition the trust to mass ratio, so it is trivial to find the thrust if we know the g-rating and the mass. From MT we know the approximate masses of standard starships as roughly 10 tonnes per Dton for unarmoured ships.

So, a Free Trader with 1 g at 200 Dt or approximately 2000 tonnes has a thrust of roughly 20 MN.

Since Traveller doesn't take mass into account that's not a valid assumption when discussing lift. Mass is vitally important. But let's run with that. You now have mass. So a free trader is massing around the weight of a fully loaded space shuttle with full fuel tank and a pair of SRB's. SSME + boosers generates about 30 MN. So the free trader is putting out 2/3rds of that. So we have established mass and force. Progress!

No, anti-grav does not nullify gravity, just provides a force to offset it (lift), and that force is vectorable (just as M-drives) so it can provide forward thrust, not just lift.

The anti-grav drive must still be dimensioned for the carried mass, as specified by Striker and MT.

As far as the vessel is concerned, the gravity is nullified. A ship (or person) utilizing antigravity can ascend, float, or descend. Isn't that the definition of nullify, to cancel out the effect (of gravity)?

No, anti-grav does not imply inertialess drive. That would be much more magical mere M-drives...

Never stated nor implied anything about inertialess drive. This discussion is complicated enough without trying to toss out another concept.

But that is quite unnecessary. A thousand times as large a ship with a thousand times as large a drive (as specified by the drive percentages) producing a thousand times as much thrust would have the same thrust to mass ratio hence g-rating and would accelerate at the same rate. And the same for a trillion times as large a ship. No anti-grav needed, nor would it affect the mass of the ship hence the acceleration in space.

Assumes a purely scalar model, which we know isn't true. Getting back to the concept of lift there are inverse laws that apply. In Traveller terms your drive rating is based upon volume, not mass. And, as stated above (including your citation of MT for defining mass of an unarmored starship, MASS is required as part of the formula. A 200 Dton ship that is unarmored weighs 2,000 tons. A 200 Dton ship with armor 15 weighs 15x that? Yet the drives are the same. Ergo the scaling explanation fails.

Yes, anti-grav would be very convenient, but it is an unnecessary complication. Just like an aircraft that can land vertically, it is possible and can be useful in some specific roles, but generally it is unnecessary and to expensive for general use.

Spacecraft users would be utter fools to include anti-grav drives, since by MT they cost about as much tonnage, power, and money as an M-drive of the same rating. So, instead of a 1 g M-drive and a 1 g anti-grav drive you could just as well have a 2 g M-drive that worked everywhere, not just in a planetary gravity well.

And as I have tried to argue all along, a 2 g M-drive can be very useful, but can also be rather expensive...

How is it unnecessary? It makes the entire discussion needless since antigrav allows all ships to maneuver as one would expect them. It makes... sense. Common sense to be precise. And there is no needed additional expense as you could simply state the cost is included in the cost of the hull. The hull cost is already quite amorphous thus a single sentence would make this entire thread pointless.

MT is one version of Traveller. That design system provided more detailing of the process. However nowhere has it been stated that the rules explicitly state ships do not possess anti-gravity systems. The preponderance of evidence (illustrations & art work being the primary) would indicate that without antigravity the starports would not be possible due to the inability of ships to land or takeoff. More space would be required to take off and land. And without lift how do starships get off/on to their neat little landing pads? Are you proposing all ships are tail sitters? That would actually work, except we know from the illustrations that this isn't the case.

I'm not saying it, MWM is specifically saying it.

Note that the standard Scut does not need it since it already have a 2 g M-drive.

He can state anything he wants, still doesn't make it possible. 2G drive still doesn't generate lift, just provides more thrust. If we are back to the lifting body example you'll notice that LIFT is still predicated upon the craft being able to follow the rules of physics. Lift has to overcome drag and gravity.

 

[Anonymous]

the type R has large vents in the front of the wings for fuel scooping. it's not impossible that air can go in there and out somewhere else, thus reducing the wing's drag.

with those vents, type r fat trader looks like a space shuttle, a plane that re-enters and glides much faster than a jet fighter. i can handwave it operating without antigrav if you put wheels on it, though it seems stupider than using antigrav.

on classic traveller where i live, i remember the type r can't land. not streamlined. i could be wrong there.